This research project will investigate the following aspects of hepatic excretion of anionic drugs: 1. The hepatic excretion of iopanoic glucuronide which is the only biliary metabolite of the cholecystographic agent iopanpate. 2. The effect of pharmacological inducers and inhibitors of metabolic activity on the excretion of iopanoic glucuronide. 3. The determination of that fraction of bile flow with which the excretion of iopanoic glucuronic and iopanoate is associated (bile salt independent or bile salt dependent). 4. The characterization of the anionic transport mechanisms by the use of competition studies between iopanoic glucuronide and phenolphthalein glucuronide. These studies will use whole animal as well as isolated liver perfusion techniques. Standard hepatic and renal clearance experimental procedures will be used. Excretion rates, maximum transport rates (Tm), tissue content, metabolism, and plasma decay rates will be measured. Competition for transport sites, and the kinetics of such competition between several anionic drugs will be studied using the isolated perfused rat liver. In all experimental procedures the analyses will distinguish quantitatively between parent compound and conjugate. The data obtained from these studies will significantly contribute to the understanding of the pharmacokinetics of anionic drugs that are primarily excreted by the liver. These anions include both diagnostic and therapeutic agents currently in wide clinical use.